Electronic musical instrument simulating chiff, tracker, and dynamic keying

ABSTRACT

An electrical musical instrument for simulating pipe organs, and having a natural ensemble effect, spatial tone-distribution effect, air turbulence effect, wind-pressure-change effect, tracker keying effect, piano voice keying effect, and exact differently modulated harmonic pitch registers for mutation and compound stops and chiff. Insulated gate field-effect transistors are used for switching tone and chiff frequency currents so that the change in amplitude is sigmoid during turn-on and turn-off. RC circuitry in combination with the switching insulated gate field-effect transistors permit tracker keying and piano voice keying.

Muted tates atent 1 1 1111 3,736,614

Turner 5] May 22, 1973 ELECTRONIC MUSICAL INSTRUMENT 2,989,887 6 1961 Markowitz ..84/1.24 SIMULATHNG CHIFF, TCR, AND 3,037,413 6/1962 Markowitz ....84/1.24 3,248,470 4/1966 Markowitz et a1... ..84/1 .1 DYNAMIC KEYING 3,333,042 7/1967 Brombaugh ....84/D1G. 5 [76] Inventor: William D. Turner, 108 Manchester 3,445,578 5/1969 Cunningham ....84/DIG. 5 Avenue, Moylan, Pa. 3,617,603 11/1971 Wayne et a1 ..84/1.24 X

[22] Filed: 197} Primary Examiner-Richard B. Wilkinson [21] App], NO 130,297 Assistant ExaminerStanley J. Witkowski Attorney-Woodcock, Washbum, Kurtz & Related US. Application Data M ki i [63] Continuation-impart of Ser. No. 19,641, March 16,

1970, Pat. N0. 3,647,928, which is a continuation-in- [57] ABSTRACT pan of 713594 March 1968 An electrical musical instrument for simulating pipe cloned organs, and having a natural ensemble effect, spatial tone-distribution effect, air turbulence effect, wind- [52] US. Cl. ..84/1.24, 84/DIG. 5 pressure change effect tracker keying effect, piano CB. Voice effect, and exact differently odulated [58] Field of Search ..84/1.()l, 1.22, 1.24, harmonic pitch registers for mutation and compound D1623 stops and chiff. Insulated gate field-effect transistors are used for switching tone and chiff frequency cur- [56] References Cited rents so that the change in amplitude is sigmoid during UNITED STATES PATENTS turn-on and tum-off. RC circuitry in combination with the switching insulated gate field-effect transistors per- 3,156,769 11/ 1964 Markowitz ..84/1.24 X mit tracker keying and piano voice keying. 2,486,208 10/1949 Rienstra ...84/D1G. 5 2,989,886 6/1961 Markowitz ..84/D1G. 5 21 Claims, 26 Drawing Figures PATENIfmzi'kYzzmrs SHEET 7 OF 9 CONTROL BIAS SWITCHING A? WW ELECTRONIC MUSICAL INSTRUMENT SIMULATING CIIIFF, TRACKER, AND DYNAMIC KEYING RELATED APPLICATION This is a division and continuation-in-part application of copending application Serial No. 19,641, filed March 16, 1970, now US. Patent 3,647,928 which is a continuation-in-part application of copending application Serial No. 713,594, filed March 18, 1968, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the simulation of various kinds of pipe organs.

This invention also relates particularly to electric organs exhibiting chiff.

Chiff is a transient tone of higher frequency than the fundamental tone, which appears briefly before or during the onset of the fundamental tone when the key is depressed, and sometimes as terminal transients when the key is released. Chiff frequencies may be either harmonies or inharmonics of the fundamental, and lend assertiveness and clearer identity to the sounded tones. Most prior art electric organs do not exhibit chiff.

This invention also relates particularly to electrical musical instruments wherein a player is able to vary the rates of attack and decay of individual tones, by varying the speed of depression and release of corresponding keyboard keys.

Because pneumatic or electric keying of pipe organs is positive in character, such keying does not enable the player to vary the rate of attack and decay of individual pipe tones by varying the rates of depression and release of keyboard keys. In contrast, tracker pipe organs provide such expressive control of individual, tonal attack and decay, by direct mechanical coupling between keys and pipe valves. Except for one or two makes of electronic organ in which greater pressure on a key places more of a flexible conductive strip against a rigid resistive surface, electronic organs have not provided for any kind of control of rates of attack and decay of individual tones through keying. Even in these exceptional electronic organs, the resulting patterns of tonal attack and decay are quite unlikethose of a tracker pipe organ. In addition, there is no provision for chiff.

This invention yet further relates particularly to an electrical musical instrument having piano voice keying and tone.

In general, prior art electrical musical instruments have not been able to simulate or duplicate a sustained full piano tone having the characteristic ensemble effects of pluralities of strings struck by individual felt hammers. More particularly, prior art electrical musical instruments have been unable to duplicate the control of loudness of individual tones by rate of key depression. Furthermore, the prior art electrical musical instruments have not provided piano voice keying simulating the action of a sustain pedal of a piano.

SUMMARY OF THE INVENTION This invention relates to circuits for producing chiff, and keying circuits, for an electronic musical instrument of the type disclosed in my US. Pat. No. 3,647,928. The disclosure of that patent is incorporated herein.

An object of this invention is to achieve an electrical musical instrument capable of expressive keying as a function of the speed of movement of a player actuated member. In accordance with this object, means are provided for generating a control signal in response to the speed of the player actuated member between released and depressed positions for purposes of controlling the tone and chiff generators. The means for generating the control signals may comprise RC circuits which are connected to and disconnected from a power supply in response to engagement of movable contact members and spring biased contact elements.

A yet further object of this invention is to achieve an electrical musical instrument capable of piano voice keying. In accordance with this object, switch means are provided for the tone generators which produce a percussive but sigmoid rise in amplitude of the full piano tone currents imitating the action of a felt hammer on several piano strings followed by the initially rapid then slow decay of tone currents to imitate the pattern of damped action piano strings.

The foregoing and other objects, features and advantages of the invention will be better understood from the following more detailed description and appended claims together with the drawings.

DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are circuit diagrams of piano voice keyers and tone modulators;

FIG. 1 is a circuit diagram of a wind-pressure-change simulator;

FIGS. 2 A-B are block and circuit diagrams illustrating the generation of frequencies for octave-sounding, mutation, and compound stops,

FIGS. 2 C-I-I are circuit diagrams illustrating switches and modulators;

FIGS. 3 and 4 are circuit diagrams of non-tracker keying of related tone and chiff frequency currents;

FIGS. 5 A-C are graphical illustrations of various aspects of nontracker keying; I

FIG. 6 is a schematic diagram of a dynamic keyer;

FIG. 7 is a circuit diagram of a tracker keyer;

FIG. 8 is a schematic diagram of a modulator;

FIG. 9 is a schematic diagram of the polarity reverser;

FIG. 10 is a schematic diagram of a dynamic keyer;

FIG. 1 l is a schematic diagram of a tracker keyer for keying both main tones and initial chiff and/or terminal transient tones;

FIG. 12 is a schematic diagram of a buffered sigmoid switch; and

FIGS. 13 A-C are schematic diagrams of tracker keyer couplers.

DESCRIPTION OF A PARTICULAR EMBODIMENT The circuits which will now be described can be used with the electronic musical instrument shown in my US. Pat. No. 3,647,928.

The circuit shown in FIG. 1A provides expressive keying, natural piano tone attack and decay, and the full piano tone of a piano having from two to four strings for each note. In the figure, it will be observed that a double-switch 300, a capacitor 302, and resistors 304 and 306 comprise the turn-on section of a dynamic keyer which, in this instance, effects keyed differences in loudness of individual notes by virtue of the fact that the threshold of a transistor 308 and the values of its related components are selected so that the maximum possible gate voltage lies within the upper linear portion of the characteristic of the transistor 308 within its switching interval.

With the keyboard key fully released, the gate of the transistor 308 is biased by a power supply 321 below the thresholdof the transistor 308, so that none of the continuous tone currents across a resistor 310 appears across a resistor 312 and in modulators 314, 316, 318 and their outputs. Also, a diode 320 is biased so as to be non-conducting unless a voltage on its cathode exceeds the voltage E1 of the power supply 321.

When the key is depressed, the voltage output of the dynamic keyer quickly charges a capacitor 322 across the diode 320 and a resistor 322, the negative pulse from the capacitor 322 charge current is coupled through a diode 324 so as to charge a capacitor 326 quickly, and thence through a resistor 328 to the gate of the transistor 308 which is turned on, providing a percussive but sigmoid rise in the amplitude of the tone currents across of the resistor 312 and, in complexly modulated form in the modulator outputs, in imitation of the action of a felt hammer on several piano strings. The charge on the capacitor 326 begins at once to decline exponentially at a relatively rapid rate at first across resistors 323 and 334 in parallel, until the voltage on the cathode of the diode 320 is less then the voltage El, from which point the decline proceeds much more slowly across the resistor 334 alone, until the voltage across the resistor 334 passes below the threshold of the transistor 308; the amplitude of the tone currents across the resistor 310 and in the modulator outputs declines accordingly. These actions duplicate the characteristic, initially rapid and subsequently slow, decay of a sustained piano tone.

If, before the threshold of the transistor 308 is reached, the key is released, the charge on the capacitor 322 declines very rapidly (through a diode 336 and a resistor 338) as do also the corresponding charging currents and voltage drop. The resistor 334 and a capacitor 340 coupled to the gate of the transistor 308 causes the gate voltage to decay slowly enough to imitate the action of a felt damper on piano strings.

FIG. 1B differs from FIG. 1A only in involving a conventional regenerative switch (transistor 341 and 343 and associated components, 344, 346, 348, 350 and 352) which is held on by a switch 354 functioning as a piano sustain pedal. Thus, if at first only the sustain pedal 354 is depressed and is then held down, the voltage E2 from a power supply 356 will be coupled only to the emitter and base of the transistor 340 and to the collector of the transistor 342, but no further, since neither the transistor 340 nor the transistor 342 is thereby turned on. If, however, the keyboard key on switch 300 is then depressed as well, the transistors 340 and 342 will turn on and the amplitude of the corresponding tone currents in the modulator outputs will decline exactly as described above as long as the key or the pedal remains depressed. If the key is depressed, held down until the pedal is also depressed, and then released, the same pattern of decline will occur as long as the pedal remains depressed. All these actions correspond to those of a piano key and sustain pedal.

Representative component values for the circuit of FIGS. A and 10B are listed below:

352-570K Capacitor 302-25 Capacitor Diode Grossly inadequate wind pressure in a pipe organ will produce unpleasant changes in pitch and exaggerated ensemble effects as larger numbers of pipes are sounded. With generally adequate wind pressure, slight and pleasant changes in pitch and ensemble effects occur with the speaking of many pipes. Such changes are produced in the electrical musical instrument by the circuit shown in FIG. 1, which places the drainsource circuit of a MOS transistor 400 across resistor 550 in FIG. 2E, or of two different MOS across resistors 600 and 602 in FIG. 2H. The effect of activating one or more of the illustrative stops is to increase the voltage across 402 of FIG. 1, until at maximum this voltage is slightly less than the threshold voltage of the transistor 400. The effect of depressing one or more of the illustrative keyboard keys is to increase further the voltage across the resistor 402 and on the gate of the transistor 400 in FIG. 1. Increasing the voltage beyond the threshold renders the drain-source circuit increasingly conductive. A capacitor 404 buffers these changes, to eliminate noise effects. The increasing conductivity of the transistor 400 raises the frequency level of the subsonic frequency band passed by the phase shift filter, and produces more rapidensemble effects and correspondingly greater Doppler-effect changes in the pitch of tones sounded by the instrument. In general, unless a sufficient number of stops are activated, depressing even large numbers of keys will have little or no effect. Similarly, activating stops will have no effect unless a sufficient number of keys are also depressed.

Smaller values of resistors 406, 408 and 410 can be used for heavier-voice stops, and smaller values of resistors 412, 414 and 416 can be used for lower pitched notes. A single stop and keying resistor network for the entire instrument, like that shown in FIG) 11, suffices to serve a different transistor 400 for each subsonic frequency filter in the instrument.

Representative component values for the circuit of FIG. 1 are listed below:

Resistor Transistor FIG. 2A presents essential portions of an illustrative instrument for producing compound stops as well as mutations and octave-sounding stops, as in a straight organ free from octave coupling or other plural functioning of given ranks of pipes. For simplicity of exposition, FIG. 2A shows only the A-notes of four adjacent octaves of a nine-octave instrument. FIG. 2A differs from FIG. 1A of my US. Pat. No. 3,647,928 in presenting illustrative filters, F, which produce (tertiary) sine waves of chromatic and achromatic frequencies from the (secondary) square waves which are derived from the (primary) tone oscillator sine wave outputs. For purposes of the present illustration, it is assumed that the wave shapers, W, produce (fourth-order) diapason tone frequencies from the tertiary waves.

FIG. 2A also shows that, in order to effect simultaneous articulation of all voices and registers activated by any given keyboard key, each key actuates a single control section, Sc, of a sigmoid switch, which in turn controls a plurality of switching sections, Ss, of such switches shown in detail in FIG. 2F. The sigmoid switching sections are coupled to the keyed control sections in such a way that the keys actuate the desired pitch registers. Thus, in the 8' Principal stop, each switching section receives the tone frequencies from the first-harmonic wave shaper in the same octave, and the control current from the sigmoid control section in that octave. The 2 Nazard mutation stop is the same except that its switching sections receive the tone frequencies from the third-harmonic wave shapers in the same octave.

The 4 Octave stop switching sections receive their switching currents from the switch control sections of the same octave, but receive the tone frequencies from the first-harmonic wave shapers of the next higher octave, thereby providing the second harmonic. It is evident that the switching sections of an 1 a Quint stop would similarly receive the control currents from switch control sections in the same octaves, but the tone frequencies from the third-harmonic wave shapers in the next higher octaves, thereby providing the sixth harmonic.

For simplicity of illustration, FIG. 2A shows the connections for the A key only, for the illustrative Cornet de Recit, compound stop. In this limited illustration, it will be noted that all the switching sections receive the control voltage from the switching control section of the A key, while receiving eight different tone frequencies provided by various wave shapers at various pitch registers and octaves. Wave shaper outputs are used in the same manner to produce other notes, and the multiple voices of manual keyboard mixture stops. Notes repeated because of mixture breakbacks will not fuse into single louder tones, but will be differentially modulated stereophonically, since, although keys in the same or different octaves can repeatedly activate the same frequencies having the same or different wave forms there are different modulations of frequencies at different pitch registers in the same octaves as well as of frequencies at different pitch registers in different octaves.

FIG. 2A shows the outputs of the switching sections as paired. This pairing is achieved by the imbalancers (resistors 18-21, inclusive) shown in FIG. 2F. These imbalancers produce paired outputs of unequal amplitudes from the single outputs of the wave shapers, W, shown in FIG. 2A. The differences in amplitude lend the different tones different general locations in space as in a pipe organ.

The paired outputs of the switching sections in FIG. 2A go to modulators, M, (shown in FIG. 26) whose corresponding sources of subsonic frequency currents are shown in the separate FIG. 2B for purposes of clarity. It is evident that all waveforms in a given octave in FIG. 1A of my US. Pat. No. 3,647,928 are modulated by a single modulation unit for that octave. In contrast, in the system illustrated in FIG. 2A, each separate register of each waveform in each octave is modulated by its own separate modulator. (Not shown in FIG. 2A are other possible waveforms than the illustrative one, and the fact that for a given stop the outputs of all switching sections for all pitches or notes of a given register and waveform in a given octave go to the same modulator for common modulation.) It will be observed, of course, that there are no separate voice modulator units in FIG. 2A. Instead, in FIG. 2A, each modulator serves both as an octave and pitch register modulator, and voice modulator, as indicated in the illustrative circuit shown in FIG. 2B. FIG. 2B shows the same modulators shown in FIG. 2A, but only the connections of these modulators with their paired, subsonic frequency sources.

In FIG. 2B, the single lines which connect paired outputs of filters, (see also FIGS. 2E and 2H), to the A or B pairs of inputs of the modulators, M (see also FIG. 26) actually signify paired connectors. They are shown as single lines in order to simplify the block diagram. Thus, FIG. 2B shows that each modulator receives at its A and B pairs of inputs altogether two sets of paired outputs of subsonic frequencies, from pitch register filters and voice filters, respectively. It is apparent that, since two different subsonic pass-band filters and frequency sources are thereby coupled to each modulator, each such modulator will receive a total resultant pattern of subsonic frequencies different from the total resultant pattern of such frequencies received by every other modulator in the instrument.

The matrix comprised by such an array of modulators and different subsonic frequency sources underlies the present referance to such modulation as matrix modulation. Although matrix modulation requires a modulator like that shown in FIG. 2G for each keying of each octave of each pitch register of each voice, it requires only as many filters as there are a) different keyed octaves of different pitch registers, and b) different voices, altogether, and it requires still fewer basic sources of subsonic frequencies since the same source can supply different bands of such frequencies to different filters. A random noise generator is shown in FIG. 2C as such a source. When the modulation frequency of 6-16 Hz is generated and applied to the modulation, the subtle sounds of air turbulence in organ pipes may be achieved.

It is evident that the filter shown in FIG. 2E provides bands of subsonic frequencies which are opposite in phase, whereas the filter shown in FIG. 2H provides bands of subsonic frequencies which move into and out of phase. Coupled to modulators M, both types of filter stereophonically produce both monaural and binaural beat effects, and corresponding ensemble effects.

The tone frequencies which the present device produces can be used as harmonic or inharmonic chiff frequencies as well as regular tone frequencies. Frequencies which are higher harmonics of one fundamental frequency are obviously inharmonics of many other fundamental frequencies. When filters yield all six harmonic families, 604 different frequencies in all are available for harmonic and inharmonic chiff, over a span of nine octaves or 108 fundamental pitches.

As shown in FIG. 2A, the paired tone outputs, X'Y, of different modulators converge to appropriate stop switches, S, which are actuated by stop tabs, ST (voice switches on the instrument console). The outputs of the stop switches, S, converge to the paired common channels coupled to the stereophonic system, for differential stereophonic modulation of different octaves, registers, and voices.

FIG. 2B shows that there is continuous pitch register modulation as long as the instrument is turned on, but voice modulation only when the modulation suppressor, MS, actuates the switches, S, (shown in FIG. 2D) which couple the voice noise generators to voice modulation filters, F.

Representative component values for the circuit of FIG. 2C are listed below:

Resistor 500- 1 K 502-K Diode 504-IN21B Capacitor 506-10p.fd Transistor 508-2N3392 Representative component values for the circuit 2D are listed below:

Resistor 510-470 5 12-470 Capacitor 5 l 4- l Opfd Transistor 5 l6-RN83 18D Representative component values for the circuit 2E are listed below:

Resistor Diode Capacitor Representative component values for the circuit 2F are listed below:

Resistor 556-470 562-l00K Transistor 564-RN83 1 8D Representative component values for the circuit 2G are listed below:

556-470K 568-470K 570-470K 572-470K 574-560K 576-560K Resistor 590-10 592-l0 594-10 596-10 598-10 601-10 Transistor 603-RN83 18D 604-RN8318D Resistor Representative component values for the circuit of FIG. 2H are listed below:

Resistor Chiff is a transient tone of higher frequency than the fundamental tone, which appears briefly before or during the onset of the fundamental tone when the key is depressed, and sometimes as terminal transients when a key is released. Chiff frequencies may be either harmonics or inharmonics of the fundamental, and lend assertiveness and clearer identity to the sounded tones.

The circuit shown in FIG. 3 keys both tone and chiff frequencies when the attack of the chiff is relatively rapid. The circuit consists simply of two sigmoid switches activated by the single key, 650, and so designed in the illustrative case that the chiff begins before the tone, and decays as the tone rises to full loudness. The chiff decays because the switching voltage for its sigmoid switch is coupled to the gate circuit of a transistor 652 by a capacitor 654 whose rapid charge and discharge across resistors 656 and 658 provide the transient turn-on and turn-off of that transistor.

The circuit in FIG. 4 affords a more gradual chiff attack as well as extended control over the loudness and duration, and the sharpness and symmetry of the attack and decay of the chiff. The action of the circuit will be described first, relative to production of a soft, brief chiff with symmetrical attack and decay.

When the key 660 is closed, capacitors 662 and 664 charge rather quickly through a resistor 666. But the charging current across a resistor 668 and the baseemitter junction of a transistor 670 turns the transistor 670 on so as to ground the voltage from the capacitor 662. As the capacitors 662 and 664 proceed to discharge across the resistor, the voltage across the resistor 668 declines and Q2 begins to turn off, enabling the voltage from the capacitor 662 to begin to appear on the gate of a transistor 672, as shown by the solid, switching voltage e, curve in FIGS. 5A and 5B. This voltage reaches a maximum when the transistor 670 is almost off, and then declines with continuing discharge of the capacitor 662. FIG. B shows the solid e, switching voltage curve passing twice through the sigmoid switching interval of the transistor 672 so as to produce across a resistor 674, currents which have been continuously coupled to a resistor 676, but in the time pattern shown in FIG. 5C. Opening the key 660 allows the electrons on the plates of the capacitor 662 to pass through a diode 678 so as to equalize their number between the plates, preparatory to the next keying.

If the keying supply voltage is reduced, or the resistance of the resistor 666 or the resistor 668 is increased, a switching voltage like that shown by the dotted e's line in FIG. 58 will produce a briefer chiff with more gradual attack and decay. Changingsuch values still further will finally cutoff the chiff entirely. Lowering the capacitance of the capacitors 662 and 664 to new, equal, smaller values will sharpen both the attack and decay of the chiff while reducing its duration. Increasing the capacities together will soften and lengthen the chiff. Reducing the value of the resistor 666 will overcome some of the shorting effect of the transistor 670, and produce a chiff with more rapid attack and slow decay.

Representative component values for the circuit of FIG. 3 are listed below:

Resistor Representative component values for the circuit of FIG. 4 are listed below:

668-100K 674-470 676-470 7l6-270K 718- 57K 720- 18K 722- 22M 724-560 726-560 728- IM 730-100K 732-100K Capacitor 662-0.1 664-01 Resistor 738- l .0 Diode Transistor While differences in pressure on piano keys produce corresponding differences in loudness of the struck notes, the mechanical action of a piano is such that it is the speed of notion of the key, produced by the dynamic pressure on it, which directly controls the loudness of the tone. Similarly, in tracker pipe organs, ex-

pressive differences in rate of attack and decay of individually keyed pipes are dependent on the speed of motion of the keys. Thus, expressive control of both piano and tracker organ tone is a direct function not of static key pressure, but of speed of key movement as effected by transient or sustained, dynamic pressure on the key. Electronic duplication of such control, therefore, requires that speed of key movement, and not pressure as such, be translated into some corresponding electrical impulse. Electronic pianos and organs ordinarily do not provide for such control.

The dynamic keyer circuit shown in FIG. 6 affords this control. It affords changes in the amplitudes of on and off keying voltages, according to the speed with which individual keys are depressed and released. The mechanical portion of the keyer consists of two physically coupled but electrically independent contacts, 750 and 752 which move together and touch four springs, 754, 756, 758, and 760 at various stages of the excursion of the key. Were the contact 752 lacking, springs 758 and 760 are so tensed as to come to rest against an immovable insulating separator 762 which is slightly thicker than the contact 752 and located at the middle of the excursion of the contact 752 but out of the way of that contact at all times. Thus, with the key released and at rest, the contact 752 touches the spring 758. As the key is depressed to the middle of its excursion, the spring 758 comes to rest against the separator 762 and breaks its own connection with the contact 752. As the depression continues, the contact 752 immediately makes connection with the spring 760 and maintains this connection as the contact 752 is further depressed by a key. Releasing the key simply reverses these effects.

The further mechanical and electrical action of the keyer is as follows. As the key is depressed, the contact 750 first touches the spring 754, placing the full negative voltage E across the resistor 764. As capacitor 766 charges, this voltage drop across the resistor 764 declines exponentially. If the further depression of the key is rapid, a higher voltage will be placed on the contact 752 when it touches the spring 760 than would be placed there following slow depression of the key and completion of the charge on the capacitor 766.

As depression continues, the contact 750 finally touches the spring 756 charging a capacitor 768. As the key is then released the capacitor 768 discharges across the resistor 770 and 772 placing an exponentially decreasing positive voltage on the upper end of the resistor 772. If continuing release of the key is extremely slow, this positive voltage will reach a minimum by the time the contact 752 touches the spring 758 so that the contact 752 will merely be disconnected from the spring 760 and then grounded by the spring 756 and the resistor 772. If as usual, however, release of the key is more rapid, the spring 756 will place on the contact 752 an exponentially decreasing positive voltage whose initial amplitude will be greater, the more rapid the release of the key. This action will accelerate the turn-off of systems coupled to the contact 752, whose oncondition corresponded to the opposite, negative polarity provided by the spring 760, and the turn-off will be more rapid, the more rapid the release of the key.

Representative component values for the circuit of FIG. 6 are listed below:

76468K Capacitor 768-25ufd Because pneumatic or electric keying of pipe organs is positive in character, such keying does not enable the player to vary the rates of attack and decay of individual pipe tones by varying the rates of depression and release of keyboard keys. In contrast, tracker organs provide such expressive control of individual, tonal attack and decay, by direct mechanical coupling between keys and pipe valves. Except for one or two makes of instrument in which greater pressure on a key places more of a flexible conductive strip against a rigid resistive surface, electronic organs have not provided for any kind of control of rates of attack and decay of individual tones through keying. However, even in these exceptional electronic organs, the resulting patterns of tonal attack and decay are quite unlike those of a tracker pipe organ, and there is also no provision for Chiff.

The circuit shown in FIG. 7 affords the effects of tracker keying of tones and Chiff in the present electrical musical instrument. The left portion of the diagram embodies a dynamic keyer like that shown in FIG. 6, with the addition of a contact 776 and a spring 778 for keying Chiff. The dynamic keyer proper turns a transistor 780 on and off as a sigmoid switch whose switching voltages and rates of response are varied by the keyer as in the discussion of FIG. 6, so as to duplicate the effects of tracker action keying of an organ pipe. The essential effect of the higher, negative and positive voltages connected to a resistor 782 by the variously moved contact 752 is to accelerate the charge and discharge of a capacitor 784, and thus to sharpen the attack and decay according to the speed with which a keyboard key is depressed and released, as in a tracker pipe organ.

The extremely brief discontinuity in the action of the contact 752 as a non-shorting switch between the springs 758 and 760 is rendered inaudible by the fact of its occurence outside the sigmoid switching interval of the transistor 780. That is, as the key is depressed, the contact 7 52 both leaves the spring 758 and touches the spring 760 while the transistor 780 is still in its subthreshold state. Similarly, as the key is released, the contact 752 both leaves the spring 760 and touches the spring 758 while the transistor 780 is still in its ohmic state. Neither of these actions affects the conductivity of the transistor 780 and, therefore, both actions remain inaudible throughout the entire sounding of' a note.

With regard to tracker action keying of Chiff, it can be seen in FIG. 7 that depression of the key causes the contact 776 to touch the spring 778 and to turn on a transistor 786 slightly before the contact 752 touches the spring 760 and turns on the transistor 780. This sequence causes the Chiff to sound before, at, or during the onset of the tone, as determined by the design of the transistor 780 and the transistor 786 switches. If the key is held at this point and not depressed further to enable the contact 752 to touch the spring 760, only the Chiff will be heard, as with a tracker organ pipe under low pressure from a partially depressed key. Otherwise, since the gate of a transistor 788 is coupled to that of the transistor 780, as the tone comes on full the transistor 788 will turn on with the transistor 780 so as to ground the keying voltage of the transistor 786 and, thus, turn off the Chiff.

When the fully depressed key is released, the contact 752 leaves the spring 760 slightly before the contact 776 leaves the spring 778, so that, if the key is held partly depressed between these two positions, the tone (the transistor 780) and the transistor 788 turn off, thus allowing the transistor 786 to turn on and the Chiff to sound, as in a tracker organ pipe under reduced pressure from a partly released key. If instead, as is normally the case, release of the key is continued, the contact 776 leaves the spring 778 and cuts off the keying voltage to the transistor 786 before the Chiff becomes audible. With tones having prominent terminal transients, the transistor 788 can be selected for a higher threshold so that it will turn off more quickly than the transistor 780, and so allow the Chiff to sound more emphatically with decay of the tone.

The values shown below for the components in the FIG. 7 circuit are illustrative for a flute tone having a fairly prominent third-harmonic Chiff which sounds clearly before the tone proper is heard. Selection of other values for other amplitudes and time relations of Chiff frequencies follows routine design procedures for sigmoid switches.

Resistors FIG. 9 shows a polarity reverser which enables the opening and closing of a single-pole single-throw switch 816 to reverse in an output E, the polarity of direct currents which are coupled to an input 13,. Closing the switch 816 places on the high side of the output the input polarity which is coupled to the drain of the mosfet transistor 818 or 819 which the closed switch turns on. Since the other pole of an input is coupled to the common input connection C,, it will appear at the common output connection C In FIG. 9, the two transistors 818 and 819 have their gates coupled together, and their bodies (substrates) coupled to the (common) ground. It will be seen that, when turned on, either transistor will couple the output of its source to the source of the other, off-transistor whose channel has the same polarity as that output. Although these identical polarities allow the coupled currents to pass thesource-body junction which is therefore forward-biased for them, the diodes 821 and 822 which couple the bodies to the common ground are reverse-biased for them so as to prevent the source of the off-transistor under consideration from shunting the output of the source of the on-transistor to ground.

The forward-biasing of the off-transistor relative to the output of the on-transistor reverses the polarity of the body of the off-transistor in its channel region so as to tend to place the transistor in a conducting condition just as would its normal gate voltage, and thus to op-' pose the output of the on-transistor with the input potential of the off-transistor. However, the potential on the gate of the off-transistor is not zero, but a value of opposite polarity absolutely equal to that which normally turns the transistor on. If the absolute value of this gate voltage has such polarity and potential, it will induce in the channel the same polarity as has the rest of the body. This channel polarity keeps the drain and source of the off-transistor mutually uncoupled and, thus, maintains the off-transistor in an actual offcondition. In other words, while the off-transistor is nominally an enhancement mode transistor, when it is off in the present configuration it functions as a depletion mode transistor with a threshold. The diode which couples its body to the ground is still necessary to such functioning since the depletion effect merely acts upon the channel region to make its polarity that of other regions of the body.

The duration of the reversal process is a direct function of the mosfet transistors turn-on delays and rise times, and turn-off delays and fall times, and is usually of the order of 100 to 200 nanoseconds. The very high impedance of the mosfet gate inputs enables the currents appearing across resistor 820 to be fanned out to large numbers of mosfet pairs so as to enable each pair to reverse its own input polarities.

FIG. shows a dynamic keyer having a single moving contact 750 which touches three springs 754, 755, 756 in that order when the contact is lowered, and breaks contact with these springs in the reverse order when the contact is raised. Two of these springs 754, 756 are coupled to two RC networks A (that is, capacitor 766 and resistors 774,764) and B (that is, capacitor 768 and resistors 770, 772) just as in FIG. 16. However, the intermediate spring 755 in FIG. is coupled to the gates of two polarity-reversing, enhancement mode mosfet transistors 818, 819, and the currents appearing across resistors 764 and 772 are coupled to the corresponding inputs of the reversing transistors.

The action of the keyer is as follows. When the contact 750 is in a fully raised position and thus touching none of the three springs, there are no currents at B, because transistor 818 is held off by the positive, gate bias voltage and the E terminal is grounded by the ontransistor 819 across resistor 772. When the contact 750 is lowered against spring 754, capacitor 766 quickly charges negatively so as to place at first a high negative potential across resistor 764. This potential then declines exponentially to equal that supplied by the voltage divider consisting of resistors 774 and 764. Lowering the contact further so as to touch also spring 755 reverses the polarity on the two transistor gates so as to turn transistor 819 off and to allow transistor 818 to couple to the higher E terminal the negative currents across resistor 764 and whose magnitude will depend on the speed with which the contact is lowered to spring 755 from the fully raised position.

As the contact 750 is then lowered further so as to touch also spring 756, capacitor 768 quickly charges. However, the negative voltage across resistor 772 cannot reach the higher output terminal because transistor 819 is held off by the negative keying voltage from spring 755 and on its gate, and only the negative currents across resistor 764, coupled by the on-transistor 818, remain on the higher E terminal. When, now, the contact 750 is raised so as to break its connection with spring 756, the resulting discharge of capacitor 768 places an initially high positive voltage across resistor 772, and whose magnitude declines exponentially to zero. If contact 750 is raised further so as to break also its connection with spring 755, transistor 818 will be turned off so as to uncouple negative currents from resistor 764 to the higher E terminal, and transistor 819 will be turned on so as to couple to that terminal any positive currents remaining across resistor 772. If by that time capacitor 768 has lost all its positive charge, the higher E, terminal will simply be grounded through transistor 819 and resistor 772, as originally.

Thus, the dynamic keyer in FIG. 10 delivers the same, changing and reversing currents as does the keyer shown in FIG. 6, yet does so with only a single moving contact and with more rapid and positive reversal of the keyed polarities.

FIG. 12 shows a buffered sigmoid switch having the gate of a negative channel, depletion-enhancement mode mosfet transistor 844 coupled to the output terminal (in this instance, the drain) of the positive channel, enhancement mode switching mosfet transistor 843. Resistor 842 has extremely short leads to the drain of transistor 843, the gate of transistor 844, and the ground, so as to minimize currents induced across it by ambient electromagnetic fields. This enables minute currents to be switched by transistor 843 and amplified by transistor 844 without intrusion by such induced currents.

FIG. 11 shows a tracker keyer for keying both main tones and initial chiff and/or terminal transient tones exactly as by the tracker action of a pipe organ, and for controlling the loudness and temporal extents and relations among all such tones. The left portion of FIG. 11 shows a dynamic keyer coupled by two buffer transistors 823, 824 to the two transistors 818, 819 of a polarity reverser. The buffer action enables the output of the reverser to be fanned out to large numbers of sets of sigmoid switches without appreciably altering the load on the RC networks of the dynamic keyer. (Transistors 744 and 745 and their associated components comprise a regenerative switch which is discussed below.)

The output of the buffered dynamic keyer is shown coupled to the keying resistor 782 of a sigmoid switch control section having two RC output networks (resistor 804/capacitor 814, and resistor 792/capacitor 784) whose time constants can be adjusted relative to each other so as to vary the respective onsets of chiff and main tones and the suppression of chiff. The first RC network (804/814) is shown coupled to the gate of a chiff-switching transistor 786 whose body (substrate) is grounded and whose threshold is therefore normal for that transistor. The second RC network (792/784) is coupled to the gate of a main-tone switching transistor 780 whose threshold is raised slightly above that of chiff switching transistor 786 by placing a small positive bias on its body. This higher threshold causes a main tone to begin sounding shortly after the onset of a chiff tone, while the capacitors 814 and 784 are being charged by the switch control section. The second network (792/784) is coupled also by a forward-biased diode 831 to the gate of a chiff-suppression transistor 788 whose body is also positively biased to raise its threshold usually beyond that of the tone-switching transistor 780, so that it begins to turn on more or less near the completion of onset of the main tone, and so as to ground the gate of the chiff-switching transistor 786 and, thus, to turn off the chiff tone and hold it off as long as the main tone is sounding.

In the absence of the indicated regenerative switch (transistors 744, 745 and related components), release of contact 750 and decline of the switching voltages on the RC networks 804/814 and 792/784 would first turn off the chiff-suppressing transistor 788 so as to turn on the chiff-switching transistor 786, then to turn off the main-tone switching transistor 780 and finally the chiffswitching transistor as well. The same result would follow if the regenerative switch were present but the diode 830 forwardly biased by it were placed at ground. Either way, release of contact 750 would first insert the chiff into the main tone, and then turn off the main tone and then the chiff.

Some organ pipes manifest such terminal as well as the initial transient tones, and are simulated by the tracker keyer functioning as just described. However, other organ pipes manifest no such terminal transients. The latter pipes are simulated by placing the cathode of diode 830 above ground potential on resistor 747 and at a voltage definitely above the threshold of chiffsuppressor transistor 788. Under these circumstances, when contact 750 is in a fully released position, no current reaches the regenerative switch, and the cathode of diode 830 is at ground. When the contact is lowered so as to touch spring 754, negative keying current is coupled to the regenerative switch so as the prepare it for triggering but not to trigger it. Thus, the cathode of diode 830 still remains at ground, but since it is reversebiased for negative switching currents across capacitor 784, transistors 788 and 786 will function as described above, to sound the chiff briefly as contact 750 is lowered.

However, when contact 750 touches spring 756, the regenerative switch is triggered, a supra-threshold negative current appears across resistor 747, on the diode 830, and on the gate of chiff-suppressor transistor 788. This current holds transistor 788 on, and the chiffswitching transistor 786 off, until complete raising of contact 750 breaks its connection with the regenerative switch and therefore with the chiff-suppressing transistor. Of course, at this point, the chiff still does not sound, since the switching currents will have been uncoupled from the gate of chiff-switching transistor 786. Thus, under the condition just described, the onset of the main tone will be accompanied by an initial transient tone, or chiff, while the decay of the main tone will not be accompanied by a terminal transient tone.

Just as the amplitude and the temporal properties of initial transients can be varied by altering the amplitudes of chiff-frequency currents coupled at the connection C to resistor 810, and by altering the positive bias on the body of transistor 788, so the amplitude of terminal transients can be increased by placing the cathode of diode 830 nearer ground potential on resistor 747, and decreased by placing it farther from ground potential on that resistor.

FIG. 11 shows the tone frequency outputs (drains) of the transistors 780 and 786 coupled to a common buffer transistor 834, and thence by two unbalancer resistors 844 and 845 to two channels for differential stereophonic modulation.

FIGS. 13A, 13B and 13C show three different means for coupling tracker keyers between two or more keyboards. Each figure involves one illustrative key each on two illustrative keyboards. At the bottom of each figure are shown two groups of three leads each, each group of which would be coupled to the remainder of its own tracker keyer circuit, just as the springs 754, 755 and 756 in FIG. 11 are coupled to the remainder of the tracker keyer in that figure. In the FIGS. 13, the switches 882 and 884 are stop switches activating the keyboards corresponding to such stops, while the switches 883 couple one keyboard to another. If stops are not required to activate given keyboards, all switches 882 and 884 may be by-passed as may also be the A and C switching devices in FIGS. 13B and 13C.

FIG. 13A signifies replication of contacts 750 on any key which is to activate a key on another keyboard. FIG. 13B couples the springs associated with contact 750A to those associated with contact 750C, by means of a multi-contact relay (or switch, in organ terminology) 900B activated by switch 883. FIG. 130 substitutes sets of mosfet DC switches for such relays. In this figure, the ground connections of the mosfet bodies, necessary to their indicated function, are omitted from the illustration for reasons of simplicity.

Representative component values for the circuit of FIG. 9 are listed below:

Resistor 817-1OK 820-560K Diode 82l-1N54A 822-1N54A Transistor 8 l 8-2N4352 8l9-2N435l Representative component values for the circuit of FIG. 10 are listed below:

820-560K Capacitor 776-1 821-1N54A 822-1N54A Resistor Diode Transistor Representative component values for the circuit of FIG. 12 are listed below:

841-56 ohms 842-K Capacitor 814-.015 Transistor 834-MFE3004 Resistor Representative component values for the circuit of FIG. 11 are as follows:

Resistor 810-68 ohms 829-39 ohms 739-IN54A 740-IN54A 823-MFE2002 824-MFE2001 834-MFE3004 Representative component values for the circuit of FIGS. 13A, 13B and 13C are listed below:

FIG. 8 shows a modulator providing random, differential, monophonic and stereophonic modulation of given tones, and having an adjustable ratio between its monophonic and stereophonic modulations of those tones. It consists of two modulator units A and B which are similar except for the illustrated polarities of their modulating transistors 862A and 8628, and whose respective modulating currents are intercoupled by resistor 870 and capacitor 871. Adjustments are provided for combined and independent control of levels of modulation, for setting original and amplified modulating currents at appropriate points within the switching intervals of transistors 855 and 862, for high amplitude modulation at low subsonic frequencies for monophonic and stereophonic ensemble effects, and for low amplitude modulation at higher subsonic frequencies for simulation of air turbulence effects. Buffered outputs of the modulating transistors are further amplified for coupling to stereophonic channels.

In FIG. 8, potentiometer 845 can vary the voltage on the reverse-biased noise diodes 848, while capacitor 846 prevents unwanted mixtures of random noise frequency currents between the two or other modulator units. Except for the mentioned polarities of transistors 862A and 8628 and for the intercoupling by resistor 870 and capacitor 871, the two units are essentially similar. The function of each can be considered, first independently of the other, and then the effects of the intercoupling can be indicated.

Resistor 847 is selected to control the general level of amplitude in its unit. Isolating resistor 886 and capacitor 850 couple a portion of all but the extremely low frequency random subsonic currents across resistor 849 to capacitor 887 which shunts all but the remaining, high amplitude, low subsonic frequencies to ground. These passed frequencies, essentially unaffected by capacitors 851 and 889, are coupled to the gate of transistor 855 by capacitor 888 as modulating currents productive of ensemble effects. Resistor 885 couples another portion of the random frequency currents across resistor 849 to capacitor 851 which passes only a range of low amplitude, high subsonic frequency currents together with the sonic and supersonic frequency currents. Of these currents, capacitor 889 shunts all but the higher subsonic frequencies to ground. These subsonic frequencies, which resistors 885, 886 and capacitor 888 effectively isolate from capacitors 850 and 887, appear on the gate of transistor 855 as modulating currents productive of air turbulence effects.

From FIG. 8, it is apparent that each unit, if operating independently of the other, would modulate at various subsonic frequencies the currents which are coupled to its resistor 863, so that these currents would appear in randomly changing amplitudes in the stereo channel to which its resistor 869 is coupled. The modulations of two such independent units would also move randomly into and out of phase, so that a continuous tone frequency current coupled to the two resistors 863 would result in a stereophonically heard tone having changes in both loudness and lateral position.

Under such conditions, the total instantaneous radiated energy from acoustically uncoupled speakers would be minimum when the modulated tones are equal and minimum in loudness, and maximum when the tones are equal and maximum. When the tones are equal and intermediate in loudness, or when they are unequal in loudness, the total radiated energy will lie between maximum and minimum values. Thus, inequalities in the radiated energy between the two speakers can cause changes in loudness if one energy level changes while the other remains constant, but such change in loudness are at greatest half those produced by simultaneous increases or decreases in the energy levels of the two speakers. While the resulting stereophonic changes in the spatial location of the beard tone are like those of two (slightly mistuned) organ pipes laterally separated in space, the monophonic changes in the loudness of the beard tone are like those of two such pipes placed very close together. Therefore, in given environments of an electronic organ or other instruments using the modulator in FIG. 8, it may be desirable to reduce the ratio of the amplitude of monophonic modulation to the amplitude of stereophonic modulation, or the mono-stereo ratio, below that effected by independent modulator units. Selection of resistor 870 and capacitor 871 can produce the desired ratio.

If the impedance of resistor 870 and capacitor 871 were equal to zero, the gates of transistors 862A and 8628 would be completely intercoupled, and the effects of changes of modulating currents in one direction across one resistor 856 would be cancelled by the effects of modulating current changes in the opposite direction across the other resistor 856. To change the voltages on the gates of the modulating transistors 862A and 862B, such changes of currents across the resistors 856 must be in the same direction. However, since transistors 862A and 862B are of opposite polarity, any change in voltage common to the gates of both will tend to turn one on and the other off. Therefore, the total sound energy radiated by the two speakers together will remain constant but will divide itself between the two speakers differently from moment to moment, and there will be only stereophonic modulation and lateral movement of the sound, and no monophonic modulation or change in its over-all loudness.

Intermediate impedances of resistor 870 (with that of capacitor 871 held small for balanced intermodulation by the higher and lower modulating frequency currents) will provide any desired mono-stereo ratio, with the ratio being a direct function of the impedance of resistor 870.

If a desired ratio of stereophonic modulation to a given level of monophonic modulation is to be obtained, transistors 862A and 862B may be selected to be of the same polarity and the impedance of resistor 870 can be set for the desired stereo-mono ratio.

Representative component values for the circuit of FIG. 8 are listed below:

Resistor Diode Transistor While particular embodiments of the invention have been shown and described, it will, or course, be understood that various modifications may be made without departing from the principles of the invention. The appended claims are, therefore, intended to cover any such modification within the true spirit and scope of the invention.

What is claimed is:

l. A pair of sigmoid switches for achieving chiff in an electrical musical instrument comprising:

a pair of insulated gate field-effect transistors having gate, drain, body and source electrodes and a sigmoid relation between the controlling gate voltage and the controlling drain voltage,

means for applying exponential change in voltage to said gate electrode of one of said transistors which varies between a minimum level and a maximum level,

means for applying a tone frequency signal to said source electrode of said one of said transistors,

means for applying an exponential change in voltage to said gate electrode of the other of said transistors which varies between a minimum level and a maximum level in a manner different from the voltage applied to said gate electrode of said one of said transistors,

means for applying a chiff frequency signal to said source electrode of said other of said transistors, and

means for combining the output signals being developed at said drain electrodes of said pair of transistors, said combined output signals forming a signal representing a transient tone and a fundamental tone with the transient tone appearing before or during the onset of the fundamental tone.

2. A dynamic keyer for an electrical musical instrument comprising:

a player actuated switch having released and depressed positions, and contacts between said released and depressed positions,

tone switch means having a gate input for applying a tone to said electrical musical instrument,

a bias voltage, and

a capacitive network, said bias voltage being connected through one of said contacts to said capacitive network when said switch is actuated to produce a changing voltage across said capacitive network, said last named voltage being connected through another of said contacts to said gate input so that the voltage applied to said tone switch means is dependent upon the speed of movement of said player actuated switch through said contacts.

3. The dynamic keyer of claim 2 wherein said capacitive network comprises:

a first RC circuit generating an exponentially changing voltage of one polarity as said player actuated switch is depressed;

a second RC circuit for generating an exponentially changing voltage of opposite polarity as said player actuated switch is released;

and wherein said switching means comprises a pair of complementary insulated gate field-effect transistors having a gate, drain, body, and source electrode respectively, said source electrodes providing respective input terminals for input currents of opposite polarity, said drain electrodes being interconnected to provide an output terminal for said circuit,

oppositely poled rectifying means coupling said respective body electrodes to circuit common; and

a means for applying biasing voltages of opposite polarity to said gate electrodes of said transistors to render said transistors alternately conductive from source electrode to drain electrode as said player 

1. A pair of sigmoid switches for achieving chiff in an electrical musical instrument comprising: a pair of insulated gate field-effect transistors having gate, drain, body and source electrodes and a sigmoid relation between the controlling gate voltage and the controlling drain voltage, means for applying exponential change in voltage to said gate electrode of one of said transistors which varies between a minimum level and a maximum level, means for applying a tone frequency signal to said source electrode of said one of said transistors, means for applying an exponential change in voltage to said gate electrode of the other of said transistors which varies between a minimum level and a maximum level in a manner different from the voltage applied to said gate electrode of said one of said transistors, means for applying a chiff frequency signal to said source electrode of said other of said transistors, and means for combining the output signals being developed at said drain electrodes of said pair of transistors, said combined output signals forming a signal representing a transient tone and a fundamental tone with the transient tone appearing before or during the onset of the fundamental tone.
 2. A dynamic keyer for an electrical musical instrument comprising: a player actuated switch having released and depressed positions, and contacts between said released and depressed positions, tone switch means having a gate input for applying a tone to said electrical musical instrument, a bias voltage, and a capacitive network, said bias voltage being connected through one of said contacts to said capacitive network when said switch is actuated to produce a changing voltage across said capacitive network, said last named voltage being connected through another of said contacts to said gate input so that the voltage applied to said tone switch means is dependent upon the speed of movement of said player actuated switch through said contacts.
 3. The dynamic keyer of claim 2 wherein said capacitive network comprises: a first RC circuit generating an exponentially changing voltage of one polarity as said player actuated switch is depressed; a second RC circuit for generating an exponentially changing voltage of opposite polarity as said player actuated switch is released; and wherein said switching means comprises a pair of complementary insulated gate field-effect transistors having a gate, drain, body, and source electrode respectively, said source electrodes providing respective input terminals for input currents of opposite polarity, said drain electrodes being interconnected to provide an output terminal for said circuit, oppositely poled rectifying means coupling said respective body electrodes to circuit common; and a means for applying biasing voltages of opposite polarity to said gate electrodes of said transistors to render said transistors alternately conductive from source electrode to drain electrode as said player actuated switch is alternately depreSsed and released, the same polarity being applied to both said gate electrodes at one time, the biasing voltage of one polarity producing an output current at said output terminal of a polarity corresponding to one of said input currents and a biasing voltage of opposite polarity producing an output current at said output terminal of a polarity corresponding to the other of said input currents.
 4. The dynamic keyer of claim 3 wherein said player actuated switch comprises a conductive element electrically connected to said bias voltage so as to provide a constant voltage at said element and a first spring contact means connected to said first RC circuit which is first engaged by said conductive element as said player actuated switch is depressed, a second spring contact means connected to said gate electrodes and subsequently engaged by said conductive element as said player actuated switch is depressed, and a third spring contact means connected to said second RC circuit and engaged last by said element as said player actuated switch is depressed.
 5. The dynamic keyer of claim 4 including another player actuated switch having released, and depressed positions, and contacts between said released and depressed positions, a switch means connected with said other player actuated switch and said first and second RC circuit so as to generate from said RC circuit when said switch means is actuated an exponentially changing voltage of one polarity as said player actuated switch is depressed and to generate from said second RC circuit when said switch means is actuated an exponentially changing voltage of the opposite polarity as said player actuated switch is released.
 6. An electrical musical instrument having the dynamic keying of claim 2 further comprising: a plurality of tone frequency current sources, and a plurality of modulators for modulating said tone frequency currents, said tone switch means being connected between said tone frequency current sources and said modulators and actuated in response to said voltage across said capacitive network.
 7. The electrical musical instrument of claim 6 further comprising: a plurality of chiff frequency current sources coupled to said plurality of modulators, and a plurality of chiff switch means connected between said chiff frequency current sources and said modulators for selectively applying said chiff frequency currents to said modulators, said capacitive circuit being connected to and controlling said switch means to provide tracker keying of said chiff frequency current sources.
 8. The electrical musical instrument of claim 7 wherein said plurality of switch means connected between said tone frequency current sources and said modulators and said plurality of switch means connected between said chiff frequency current sources and said modulators comprise sigmoid switches.
 9. The electrical musical instrument of claim 8 wherein said tone frequency current sigmoid switches comprise metal oxide semiconductor field-effect transistors respectively having gate, drain, body and source electrodes and a sigmoid relation between the controlling gate voltage and the controlled drain voltage.
 10. The electrical musical instrument of claim 9 further comprising a metal oxide semiconductor field-effect transistor associated with each of said tracker keyer means having gate, drain, body and source electrodes, said gate electrodes being connected to said gate electrode of said tone frequency current field-effect transistor and said drain electrode being connected to said gate electrode of said chiff frequency current field-effect transistor so as to ground said gate electrode of said chiff frequency current switch when said tone frequency current switch is fully on to interrupt said chiff frequency current.
 11. An electronic piano voice keyer for an electrical musical instrument comprising: a player actuated switch having released and depressed positions, an active Sigmoid switching device having input, output, and control terminals, a source of tone signals connected to said input terminal, a variable source of control signals connected to said control terminal in response to actuation of said player actuated switch, said source applying a sufficiently small gate control signal to said control terminal when said player actuated switch is in the released position to maintain said active sigmoid switching device below the threshold level and prevent conducting said tone signal from said input terminal to said output terminal, said source applying a first diminishing control signal to said gate terminal when said player actuated switch is initially depressed such that said active sigmoid switching device initially conducts a first diminishing tone signal from said input terminal to said output terminal, said source applying a second diminishing signal which is smaller than and diminishes more slowly than said first signal, to said gate terminal after said player actuated switch has been depressed such that said switching device subsequently conducts a tone signal, which is smaller than and diminishes more slowly than said first tone signal, from said input terminal to said output terminal, said first diminishing tone signal being followed by said second diminishing tone signal simulating the initially rapid and subsequently slow decay of a sustained piano tone, and means responsive to the rate of actuation of said player actuated switch for varying the magnitude of said first diminishing control signal in accordance with said rate.
 12. The electronic piano voice keyer of claim 11 wherein said active sigmoid switching device is a metal oxide semiconductor field-effect transistor having source, drain, and gate electrodes comprising said input, output, and control terminals respectively.
 13. The electronic piano voice keyer of claim 12 wherein said variable source of gate control signals comprises: a power supply; a charge retaining network including a chargeable means, a pair of charging circuits having different overall nonlinear resistances, and a switching means coupled to said player actuated switch for connecting said chargeable means to said power supply in response to movement of said player actuated switch to the depressed position, the initial charging current from said power supply applied to one of said charging circuits when said player operated switch is initially depressed providing said first diminishing control signal followed by a subsequent charging current through said other of said charging circuits providing said second diminishing control signal, and a control signal coupling circuit connected to said charge retaining network applying said first diminishing control signal in response to said initial charging current to said control terminal and subsequently applying the second diminishing control signal in response to said subsequent charging current to said control terminal.
 14. The electronic piano voice keyer of claim 13 further comprising another player actuated switch having released and depressed positions, said variable source of gate control signals being responsive to the position of said other player actuated switch, such that gate control signals only apply an initially first diminishing control signal followed by a second diminishing control signal when said other player actuated switch is depressed.
 15. The electronic piano voice keyer of claim 14 further comprising another player actuated switch having released and depressed positions, said variable source of gate control signals being responsive to the position of said other player actuated switch, said variable source of gate control signals only applying a first diminishing control signal followed by a second diminishing control signal when said other player actuated switch is depressed.
 16. The electronic piano voice keyer of claim 15 wherein said charge retaining network comprises a resistance meanS in series with said chargeable element, a regenerative switch in shunt with said resistance means, and another switching means coupled to said other player actuated switch for actuating said regenerative switch by connecting said power supply to said regenerative switch when said other player actuated switch is in the depressed position, said regenerative switch being actuated by depressing said player actuated switch and sustaining the piano tone as long as said other player actuated switch is depressed.
 17. An electrical musical instrument comprising: a player actuated switch having released and depressed positions, and contacts between said released and depressed positions; a main tone frequency current source; a chiff frequency current source; a modulator means for modulating main tone and chiff frequency currents from said main tone frequency current and said chiff frequency current source; a main tone switching means having a sigmoid relation between the voltage on its gate and the tone it switches, for coupling said main tone frequency current source to said modulator means, a bias voltage connected through one of said switch positions to said gate of said switching means in response to movement of said player actuated switch; and a chiff frequency switching means, having a sigmoid relation between the voltage on its gate and the chiff frequency it switches, for coupling said chiff frequency current source to said modulator means, said bias voltage being connected through one of said switch positions to said gate of said chiff frequency switching means in response to movement of said player actuated switch.
 18. An electrical musical instrument of claim 17 further comprising: a chiff suppression switching means for decoupling said chiff frequency current source from said modulator means in response to movement of said player actuated switch.
 19. The electrical musical instrument of claim 18 further comprising: a regenerative switch means for continuously actuating said chiff suppression switch means when said player actuated switch reaches the depressed position and moves through said contacts between said released and depressed positions to said release position.
 20. The electrical musical instrument of claim 19 wherein said main tone switching means comprises a first field-effect transistor and an RC network connected between said gate electrode of said first transistor and circuit common, said chiff frequency switching means comprises a second field-effect transistor and an RC network connected between the gate electrode of said second transistor and circuit common, and said chiff suppression switching means comprises a third field-effect transistor having a gate electrode connected to said second RC network and a channel electrode connected to said gate electrode of said first transistor, the substrates of said first transistor, said second transistor, and said third transistor having different biases with respect to the circuit common so as to render the first transistor conductive first, said second transistor conducted second, and said third transistor conducted third as said player actuated switch is moved from the released position through to the contacts between said released and depressed positions to said depressed position.
 21. The electrical musical instrument of claim 20 wherein said gate electrode of said third transistor is connected to said regenerative switch means. 